1. Field of the Invention
The present invention relates to swivels in tethers for animal testing and monitoring. More particularly, it relates to motorized swivels for small animals.
2. Discussion of Related Art
Animal testing is an important part of pharmaceutical and biomedical research. During such tests, the animals are placed in a cage and various devices external to the cage, such as syringe pumps, fraction collectors, electrometers, vacuum sources, light sources, and potentiostats, are connected to implants in the animal's body such as infusion cannula, ultrafiltration probes, microdialysis probes, or electrodes. The means for connecting the external devices to the implants are typically lengths of flexible, hollow, plastic tubing, flexible wires, or optical fibers. Generally, effective animal testing requires the animal to be able to function in a substantially normal manner within the cage. However, the connections to external infusion or testing devices can inhibit normal movement of the animal. In order to allow the animal to move as freely as possible, various tether systems have been developed. These systems seek to minimize the effect of the testing apparatus on the animal. The tubes or wires are hung from a point above the cage to provide a flexible connection to the animal.
A tether allows the animal to move about the cage. However, when the animal turns or rotates, the tether system can become tangled. Swivels have been developed to allow rotation of a tether so that animal movement is not inhibited and the tether continues to function properly. Such swivels may include liquid swivels with one or more lines of tubing, electrical swivels with one or more electrical or optical lines, or combination swivels with tubing and electrical or optical lines. Liquid swivels are designed so that the top and bottom half rotate independently and an internal seal connects the two halves. When the connection is electrical or optical, a form of commutator is required. For liquid swivels and swivel commutators, the lead is discontinuous, i.e., it is somehow “split” at the swivel, so that the bottom half of the lead may be required to rotate with respect to the top half of the lead. Seals are required to prevent leakage from a swivel.
Swivels can be problematic. They can be stiff and hard to turn, which limits the usefulness of the swivel. If a swivel stops rotating the animal's movement may be restricted and experimenter intervention is required to remove twists from the tether. The result is that the ideal of a stress-free environment for the animal under study is difficult or impossible to achieve with currently available equipment. Such problems are most prevalent with small test animals, such as mice, since the forces exhibited by the animal on the tether system, and hence the swivel, are small.
Some prior art equipment seeks to eliminate the problems of swivels by removing the swivel from the system. Instead of a swivel, a complex rotation system is used to prevent twisting of the tether. For example, U.S. Pat. No. 5,816,256 discloses a system for rotating a housing to prevent tangling of test leads on a test animal. The system includes a sensor assembly including two optical sensors. The tether to the animal is connected to the sensor assembly and can rotate within the assembly. However, when the tether rotates sufficiently far to activate one of the optical sensors, the cage is rotated in the same direction as animal rotation. Rotation of the cage prevents the tether from tangling and eliminates the need for a swivel. Cage rotation, however, can be confusing for an animal, as its environment is changing. Thus, the test equipment creates stimuli which can adversely affect the experiments.
In another design, U.S. Pat. No. 5,832,878 resolves the problem of stress to the animal due to rotation of the cage by providing a turntable positioned over the cage. The turntable holds all of the equipment, such as syringes or electronics, necessary for the test. Magnetic sensors are uses to detect rotation of the tether. A magnet is positioned on a tube of the tether. The tube is positioned in the center of the tether. As the tube rotates, sensors detect the rotation and operates a motor to rotate the turntable. Such a system is large, cumbersome and expensive. The rotating turntable must be large and rugged to handle the potentially significant amount of test equipment. Other prior art devices, such as U.S. Pat. No. 6,279,511 use various other turntable devices for rotating the tether and test equipment.
A need exists for a simple system for preventing tangling of tethers and to ensure proper operation of swivels in animal testing.